Abstract: The wheat inoculated with strain 43 of associative nitroge-fixing bacteria (Kleb-siella terrigena)had significantly shown high-yield result under natural conditions.The research results indicated that the reason of yield increace was the combination of the strain with the wheat root system and the presence of the bacteria cells in spaces of the roothair cells,epidermal cells an within the transportation tissues.In the heading period the nitroge-nase activity was as high as 148.8 nmol C2H4·plant-1 ·h-1,and the fixed nitrogen amount was 15.3-22.1% of the total nitrogen amount in the plant.Since the strain might release acides, the activate phosphorus content could increase by 16.1-39.7% under sand culture condition, so that the phosphorus nutrition status of the plant could be improved.In addition some hormones such as auxin,gibberellin and cytokinin existing in metabolic products of the strain could stimulate the plant to grow.It is quite evident that the reason why the wheat inoculated with the strain increases the yield is that the strain can fixe nitrogen,resolve phosphorus and produce many sorts of hormons.

Key words: Wheat, Associative nitrogen fixation, Klebsiella terrigena, Yield